Field of the Invention
The present invention relates to a computer-controlled internal combustion engine equipped with an electronically-controlled throttle system capable of electronically controlling the opening of the throttle valve, and more specifically to techniques for executing a fail-safe control routine in presence of a failure or an abnormality in a throttle position sensor located on the throttle body of an electronically-controlled throttle system and/or in an accelerator position sensor monitoring the amount of depression of an accelerator pedal.
There are two typical types of electronically-controlled throttle systems, one being a so-called half-electronically-controlled throttle system and a so-called full-electronically-controlled throttle system. The former half-electronically-controlled throttle system has a manually-wire-operated throttle valve as well as an electronically-controlled throttle valve which is commanded by an electronic engine control unit (ECU) or an electronic control module (ECM).
Usually, the electronically-controlled throttle valve is operated arbitrarily in response to an instruction of the ECU, based on engine/vehicle operating conditions, such as the amount of depression of an accelerator pedal or the like. In the presence of a failure either elsewhere in the ECU or within the sensor systems (such as, shorted/opened sensor input signals), the throttle control system switches from the full-electronically-controlled throttle system to the manually-wire-operated throttle system, so that the opening of the throttle valve is manually adjusted depending on the accelerator pedal travel. One such half-electronically-controlled throttle system has been disclosed in Japanese Patent Provisional Publication No. 7-180570.
Later models of full-electronically-controlled throttle systems utilize input informational signal data from two accelerator position sensors and two throttle position sensors. Generally, the ECU uses or selects a lower one of the sensor signals from the two accelerator position sensors byway of a so-called select-LOW process.
With respect to the throttle-opening indicative data, the ECU uses an input signal from a main throttle position sensor out of the two throttle position sensors, or selects a higher one of the sensor signals from the two throttle position sensors by way of a so-called select-HIGH process. If the failure occurs in either one of the two throttle position sensors of the duplex throttle-position sensor system, the throttle control system ordinarily de-activates the throttle actuator, so as to hold the opening of the electronically-controlled throttle valve at a predetermined "default" opening or a predetermined "fail-safe" opening, thereby putting the engine into its limp-home mode (or limp-in mode). The limp-home mode allows the engine/vehicle to be run/driven but with greatly reduced performance, (for example, the vehicle can limp in at a maximum speed of 40 Km/h). It is so inconvenient.